A solution of 5.0 103 mol L1 ascorbic acid was prepared prior to use. A stock solution of 2.5 103 mol L1 5-Br-PADAP was prepared by dissolving appropriate amount of 5-Br-PADAP in ethanol. The acetate buffers (pH 3.5–6.2) were prepared from 0.3 mol L1 acetic acid and 0.2 mol L1 sodium acetate. The water Certified Reference Materials
purchased from National Research Center for Certified Reference Materials were used for validation of the proposed method.